A major cause of sudden death in patients with heart failure (HF) is ventricular arrhythmia. Disappointingly, large clinical trials have recently demonstrated that most of the anti-arrhythmic drugs have little or no survival benefits. Surprisingly, -blockers, once thought to be dangerous and contraindicated for patients with HF, have consistently been shown to reduce the risk of sudden death. However, the molecular mechanisms underlying -blockers' survival benefits are unknown. The overall objective of this proposal is to understand the beneficial effects of -blockers and to develop novel anti-arrhythmic agents. It is well known that spontaneous Ca2+ release, also known as store-overload-induced-Ca2+-release (SOICR), can cause delayed afterdepolarizations (DADs), which in turn can trigger arrhythmias. Importantly, enhanced SOICR activity and DAD-associated ventricular arrhythmias are common in HF and in cardiac ryanodine receptor (RyR2)-associated ventricular arrhythmias. Hypotheses: the beneficial effects of -blockers are, in part, attributable to SOICR inhibition, and that SOICR inhibitors are effective in suppressing cardiac arrhythmias. Three specific aims are proposed. 1. To Assess the Impact of Different -blockers on Spontaneous Ca2+ Release or SOICR and RyR2-Associated Arrhythmias. The impact of a number of - blockers on SOICR, the activity of RyR2, and stress-induced ventricular arrhythmias will be determined using various approaches. 2. To Design, Synthesize, and Characterize Novel Carvedilol Analogues for Suppressing Arrhythmias. Our preliminary data demonstrate that carvedilol is uniquely effective among - blockers in suppressing SOICR. To improve its efficacy and to produce a novel class of anti-arrhythmic agents, a number of carvedilol derivatives will be synthesized in order to reduce or diminish its -blocking activity, while retaining or increasing its SOICR inhibition. 3. To Understand the Molecular Basis of SOICR. Site-directed mutagenesis in conjunction with single channel analysis will be used to test our hypothesis that SOICR is governed by a luminal Ca2+ sensor located within the RyR2 channel pore. Significance: These proposed studies will not only shed novel mechanistic insight into the molecular basis of cardiac arrhythmias, but also lead to the development of a new and promising class of anti-arrhythmic agents, and have direct implications for the prevention and treatment of cardiac arrhythmias.